Mechanical filter coupling



July 25, 1961 M GRNER 2,994,047

MECHANICAL FILTER COUPLING Filed Dec. 3, 1958 MANFRED B6RNER PATENTAGENT United States Patent O 2,994,047 MECHANICAL FILTER COUPLINGManfred Biirner, Ulm (Danube), Germany, assignor to TelefunkenG.m.b.li[., Berlin, Germany Filed Dec. 3, 1958, Ser. No. 777,906 Claimspriority, application Germany Dec. 11, 1957 2 Claims, (Cl. 33371) Thepresent invention relates to mechanical frequency filters and,especially, to means for varying the coupling between individualelements of the filters.

The copending application, Serial No. 693,681, filed Oct. 31, 1957,relates to a mechanical frequency filter comprising a plurality ofmechanically coupled resonant bodies to be energized in torsionaloscillation, said resonant bodies being coupled with each other by meansof longitudinally oscillating coupling lines or wires. For this purpose,cylindrical resonant bodies are suitably used which are arrangedadjacent one another with their axes mutually parallel. These bodies areinterconnected to form a ladder-like structure by means of wires servingas coupling means and running perpendicularly to the axes of the bodies.In the aforementioned application, means are disclosed for making thecoupling coeflicients between the individual resonant cylinders ofdifferent magnitude, i.e., by applying the coupling wires to suitablepoints of difierent oscillating amplitude on the individual resonantbodies.

For reasons of manufacture, it is often desirable to use stretched,substantially straight coupling wires with the result, that theadjusting means described in the abovementioned copending applicationcannot be used for adjusting the coupling coetficients.

It is an object of the present invention to obtain diiferent couplingcoetficients for the individual resonant cylinders by providing at leastone, or preferably several, resonant cylinders with a coaxial centralbore of suitable diameter. In the following, it be explained how thecoupling coeflicient depends upon the diameters of the bores through theresonant bodies to be coupled with one another, so that the coupling canbe readily adjusted to the desired value by suitably dimensioning thesebores.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and mod cations within the spirit and scope of theinvention will become apparent to those skilled in the ant from thisdetailed description.

In the drawings:

FIGURE 1 is a perspective view of a part or a system of filtersemploying difierent degrees of coupling between individual filterresonators, according to the invention;

FIGURE 2 is an enlarged end view or a resonator according to the presentinvention;

FIGURE 3 is a plan view of a to the present invention;

FIGURE 4 is a side view of FIGURE 3.

According to FIGURE 1, three cylindrical resonators 1, 2 and 3,energized in torsional oscillation, are mutually coupled by means ofcoupling wires 4, 5, 6 and 7. In this embodiment, the resonators ;1 and2 are provided with cylindrical coaxial bores 8 and 9, respectively, sothat the resonators are hollow cylindrical bodies, while the resonatorbody 3 constitutes a solid cylinder.

The coupling between two adjacent resonators is dependent upon theconstants of the material, i.e., the density p and the velocity ofmechanical propagation v, upon the cross sectional area of theresonators, the area of filter system according the system according to2,994,047 Patented July 25, 1961 ice the bores and the area of thecoupling wires. F denotes the total cross sectional area of theresonators including bore, while F denotes the cross sectional area ofthe bore, as shown in cross section in FIGURE 2. The couplingcoetficient between two adjacent resonators of the same kind can becalculated according to the following equation:

wherein the parameters relating to the material of the resonators haveno subscripts, and those of the coupling wires are provided with thesubscript k, and wherein f denotes the total cross sectional area of thecoupling w1res.

If the coupled systems have different cross sections F different bores Fand/or different properties of the material p, v, the couplingcoefiicient can be calculated with the aid of the following equation:

K in 2 pkvkfk wherein the subscripts 1 and 2 relate to the respectiveparameters of one or the other resonator.

It can be seen that the coupling coefficient between two adjacentresonators is increased when the diameter of the bore is increased inthe respective resonators.

FIGURES 3 and 4 show a system of mechanical filters comprising sevenresonators, 11, 12, 13, 14, 15, 1 6 and 17. Longitudinally oscillatingmagneto-strictive transducers 18 and 19 are provided to energize thefilter, said transducers being magnetized in a manner known per so bymeans of a permanent magnet (not shown) and being coupled to externalelectric circuits (not shown) by means of a coil (also not shown). Thebores of the outermost resonators 11 and 17 have larger diameters thanthe bores of the inner resonators, whereby the sizes of the diameter aregradually increased starting from the center resonator 114 towards theouter resonators 11 and 17. As a result of this, the coupling increasestowards the outside between the individual filter resonators, asrequired by theoretical considerations.

I claim:

1. In a mechanical tuned filter including a plurality of axiallyparallel cylindrical resonators to be energized in torsional oscillationand all resonant at the same frequency, and said resonators beingcoupled with one another by means of longitudinally oscillating couplingwires joined tangentially to said cylinders, the improvementcharacterized by providing at least one of the resonators with a coaxialbore therein, the diameter of the bore serving to determine thecoefficient of coupling be tween the associated resonator and adjacentresonators.

2. In a mechanical filter according to claim 1, at least threeresonators comprising said filter, and at least two of said resonatorshaving bores therein and arranged in such a manner that the diameters ofthe bores symmetrically increase from the center of the filter towardsthe outer ends thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,933,306 Berry et al. Oct. 31, 1933 2,552,139 Bocciarelli May 8, 19512,762,985 George Sept. 11, 1956 2,799,832 Niederman et al July 16, 19572,802,992 Doelz Aug. 13, 1957 2,810,888 George et al. Oct. 22, 19572,926,315 George Feb. 23, 1960

